Low vitamin D common even among southern teens

NEW YORK (Reuters Health) - Most black adolescents have insufficient amounts of the sunshine vitamin in their blood, even those living in the sunny southeastern US, new research shows.

About a third of white teens also had insufficient vitamin D levels, Dr. Yanbin Dong of the Medical College of Georgia in Augusta and colleagues found. And while actual deficiency of the vitamin was rare among whites -- seen in only 3 percent of girls and 4 percent of boys -- it was common for black adolescents, especially girls.

Several studies have found a high prevalence of vitamin D insufficiency in adolescents, the researchers note. However, investigations in sunnier locales have looked at vitamin D levels in the winter months, when scarcer sun means levels are lower.

To investigate how vitamin D levels vary with the seasons in more southerly US locations, the researchers looked at 559 14- to 18-year-olds living near Augusta, Georgia. Forty-five percent were black, and 49 percent were female.

Overall, the researchers found, 56 percent of the teens had insufficient vitamin D levels, defined as less than 75 nanomoles per liter of blood, while nearly 30 percent had vitamin D deficiency, meaning their levels were below 50 nanomoles per liter of blood. And in all four seasons, levels were lower for blacks than whites.

When the researchers looked at whites and blacks separately, they found stark differences. Thirty percent of white girls and white boys had insufficient vitamin D, compared to 94 percent of black girls and 83 percent of black boys. Vitamin D deficiency was seen in 74 percent of black girls and 47 percent of white boys.

None of the white study participants had vitamin D deficiency in the summer, the researchers found, but 55 percent of black study participants did. And for black girls, average levels never climbed above 50 nanomoles per liter in any season.

The researchers also found that with any measure of body composition they looked at, including body mass index, waist size, or proportion of body fat, vitamin D levels fell as fatness increased. Teens that got more vigorous physical activity had higher vitamin D levels.

Black people are believed to have lower levels of vitamin D because their more heavily pigmented skin doesn't produce the vitamin as readily as paler skin does, the researchers note. Some investigators have suggested that the greater percentage of obesity among black individuals may also be a factor.

But in the current study, race was far more influential than obesity; the researchers calculated that it accounted for 48 percent of the variation in vitamin D levels, while season accounted for just 3 percent and fat mass and physical activity counted for 1 percent each.

Vitamin D levels among teens have been declining over the past 10 to 15 years, the researchers note. "Taken together, these findings suggest that low vitamin D status is a growing national problem for adolescents in the United States, regardless of latitude," they conclude.